[NLRS] DEMI 2M Transverter using 26 MHz?

[Louis Sica]

Good point about FM below 28 MHz on most rigs. Checked the TS-590, and it
will transmit FM on 12M (checked on a Dummy load of course :) ) so I'm
suspecting it would transmit FM down to 26 MHz if "opened". It will also do
600 kHz FM splits and sub audible tones. Thanks for the heads up tho :)

-----Original Message-----
From: nlrs-bounces at mailman.qth.net [mailto:nlrs-bounces at mailman.qth.net] On
Behalf Of Dr. Gerald N. Johnson
Sent: Monday, October 15, 2012 17:12
To: nlrs at mailman.qth.net
Subject: Re: [NLRS] DEMI 2M Transverter using 26 MHz?



I can't tell from the DEMI assembly manual whether the 26 MHz IF section 
will have lower gain. There's an odd circuit that I don't understand 
instantly but mostly the IF circuit has low pass filtration, the manual 
says rolls off above 32 MHz. There's nothing in the RF section that 
would degrade weak signal performance, just maybe that odd filter in the 
IF. Even then some loss after the mixer should not affect 144.2 MHz 
performance unless its so bad the IF receiver sets the system NF. With 
17 dB rated conversion gain, the RF stage pretty much sets the system 
NF. Get down to 10 dB conversion gain and then the system NF will begin 
to suffer.

I can't tell if the two 144 MHz filters have narrow bandwidth either. 
Sent N2CEI an email but don't expect an answer for a couple weeks.

I built my first (and only) 2m converter with 26 MHz IF back about 1962. 
It still works.

As for working 2m FM, the modern HF rigs probably won't allow FM below 
28 and there is FM down to 144.390 (APRS) and repeaters in the 145 to 
145.5 MHz region. Will your IF do 600 kHz FM splits? Does it have 
provisions for subaudible tone? If not, you won't' be able to use all 
the repeaters on the band. When a Chinese handheld costs not much more 
than the special crystal for the transverter, and a decent kenwood or 
yaesu new 2m mobile costs under $130 new and has all the offsets and 
tones needed its not hard to think separate rig for FM.

I use a FT857 for HF, VHF, and UHF. It may be that I'd hear better with 
a transverter, I've not tested that option. I hear well, I think and I 
get out right now limited by my antenna not the rig. The 859 is not much 
bigger than the DEMI transverter and has more options useful from 100 
KHz to 470 MHz or wider. Its really handy to be able to tune NWS with it 
that the transverter wouldn't allow up at 162 MHz and the FM mobile will 
allow that.

73, Jerry, K0CQ

On 10/15/2012 10:13 AM, Louis Sica, Jr. wrote:
>
>
> Hello Group
>
> Contemplating (again) my possible future journeys above 54 MHz...
>
> Anyone ever use the DEMI 2M transverter using 26 MHz instead of the usual
28 MHz? I was wondering if performance degrades on the weak signal end of
the band when you do that, and if doing that even gives good performance on
the FM end of the band. Or should I just consider a seperate FM rig for
local chats?
>
> ______________________________________________________________
>
______________________________________________________________
NLRS mailing list
Home: http://mailman.qth.net/mailman/listinfo/nlrs
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:NLRS at mailman.qth.net

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html